This invention relates in general to the use of magnetic pulse welding techniques to secure two metallic components together, such as a yoke and a driveshaft tube in a vehicular driveshaft assembly. In particular, this invention relates to an improved structure for a yoke or similar end fitting that minimizes the amount of undesirable distortions that can result when a driveshaft tube is secured thereto by means of such a magnetic pulse welding operation.
In most land vehicles in use today, a drive train system is provided for transmitting rotational power from an output shaft of an engine/transmission assembly to an input shaft of an axle assembly so as to rotatably drive one or more wheels of the vehicle. To accomplish this, a typical vehicular drive train assembly includes a hollow cylindrical driveshaft tube having first and second end fittings (such as tube yokes) secured to the opposed ends thereof. The first end fitting forms a portion of a first universal joint, which provides a rotatable driving connection from the output shaft of the engine/transmission assembly to the driveshaft tube while accommodating a limited amount of angular misalignment between the rotational axes of these two shafts. Similarly, the second end fitting forms a portion of a second universal joint, which provides a rotatable driving connection from the driveshaft tube to the input shaft of the axle assembly while accommodating a limited amount of angular misalignment between the rotational axes of these two shafts.
In vehicular driveshaft assemblies of this general type, it is usually necessary to permanently secure the first and second end fittings to the ends of the driveshaft tube. Traditionally, conventional welding techniques have been used to permanently join the first and second end fittings to the ends of the driveshaft tube. As is well known, conventional welding techniques involve the application of heat to localized areas of two metallic members, which results in a coalescence of the two metallic members. Such conventional welding techniques may or may not be performed with the application of pressure, and may or may not include the use of a filler metal. Although conventional welding techniques have functioned satisfactorily in the past, there are some drawbacks to the use thereof in joining the first and second end fittings to the ends of the driveshaft tube. First, as noted above, conventional welding techniques involve the application of heat to localized areas of the two metallic members. This application of heat can cause undesirable distortions and weaknesses to be introduced into the metallic components. Second, while conventional welding techniques are well suited for joining components that are formed from similar metallic materials, it has been found to be somewhat more difficult to adapt them for use in joining components formed from dissimilar metallic materials. Third, conventional welding techniques are not easily adapted for joining components that have different gauge thicknesses. Inasmuch as the production of vehicular driveshaft assemblies is usually a high volume process, it would be desirable to provide an improved method for permanently joining these metallic components together in a manner that avoids the drawbacks of conventional welding techniques.
Magnetic pulse welding is an alternative process that has been proposed to secure the first and second end fittings to the opposed ends of the driveshaft tube. To accomplish this, a hollow driveshaft tube having an end portion and an end fitting having a neck portion are initially provided. The end portion of the driveshaft tube can be hollow to allow the neck portion of the end fitting to be disposed co-axially therein. Alternatively, the neck portion of the end fitting can be hollow to allow the end portion of the driveshaft tube to be disposed telescopically therein. In either event, an annular gap is provided between the end of the driveshaft tube and the neck portion of the end fitting. Then, an electrical inductor is provided concentrically about or within the co-axially overlapping portions of the driveshaft tube and the end fitting. The inductor is energized to generate a magnetic field that either collapses the outer member inwardly into engagement with the inner member or expands the inner member outwardly into engagement with the outer member. In either event, the high velocity impact of the two members, as well as the large pressures exerted thereon, cause them to become permanently joined together.
A typical end fitting includes a body portion having a pair of opposed yoke arms that extend therefrom in a first axial direction. A pair of aligned openings are formed through the yoke arms and are adapted to receive conventional bearing cups of the universal joint cross therein. A generally hollow neck portion extends axially in a second axial direction from the body portion. To perform the magnetic pulse welding operation, an end portion of the driveshaft tube is installed onto co-axially about the neck portion of the end fitting. When the driveshaft tube and the end fitting are assembled in this manner, an annular gap or space is defined between the inner surface of the end portion of the driveshaft tube and outer surface of the neck portion of the end fitting. An electrical inductor is then disposed about the assembly of the driveshaft tube and the end fitting. The inductor is energized to generate an immense and momentary electromagnetic field about the end portion of the driveshaft tube. This electromagnetic field exerts a very large force on the outer surface of the end portion of the driveshaft tube, causing it to collapse inwardly at a high velocity onto the neck portion of the end fitting. The resulting impact of the inner surface of the end portion of the driveshaft tube with the outer surface of the neck portion of the end fitting causes a weld or molecular bond to occur therebetween.
Unfortunately, it has been found that the high velocity impact of the end portion of the driveshaft tube onto the neck portion of the end fitting during the magnetic pulse welding operation can, in some instances, cause the yoke arms of the end fitting to be permanently deflected relative to one another. For example, if the end portion of the driveshaft tube is collapsed upon the neck portion of the end fitting, the inward deformation of the neck portion can cause the yoke arms on the other end of the end fitting to spread outwardly apart from one another. Also, the shock wave propagated through the end fitting as a result of this impact can slightly enlarge the dimensions of the openings formed through the yoke arms. These events are particularly likely to occur when the end fitting is formed from a relatively lightweight material, such as an alloy of aluminum. Such deflections of the yoke arms are undesirable because they can result in the misalignment of the respective openings formed therethrough. When the openings formed through the yoke arms are not precisely aligned, it may be relatively difficult to properly install the remaining portions of the universal joint thereon and to balance the universal joint for rotation. Thus, it would be desirable to provide an improved structure for a yoke or similar end fitting that minimizes the amount of undesirable deflections that can result when a driveshaft tube is secured thereto by means of such a magnetic pulse welding operation.